Have you ever wondered why humans don't all look the same? After all, we share a number of similarities on the inside, but on the outside we all have unique features.

The answer, according to scientists at the University of Exeter and New York University, is that some animals developed this way to deliberately avoid interbreeding.

Primates developed different facial appearances so their group was easily recognisable as being different from closely related and local species.

The reason we all look different has been revealed by scientists - it is to avoid inter-breeding. Primates were found to have developed different facial appearances so that their group was easily recognisable as being different from closely related and local species

The study, published in the journal Nature Communications, provides the best evidence to date for
the role of visual cues as a barrier to breeding across species.

WERE NEANDERTHALS WIPED OUT BY INTERBREEDING?

They are often depicted as dim-witted evolutionary losers, but Neanderthals were not driven to extinction by their lack of brains, a study suggests.

Instead, it is more likely that they disappeared 40,000 years ago because of interbreeding and assimilation with our early modern human ancestors, scientists believe.

An analysis of archaeological evidence dating back 200,000 years stripped away some of the myths surrounding Neanderthals and revealed they were more advanced and sophisticated than has widely been thought.

The differences between the two human sub-species are not enough on their own to account for the demise of the Neanderthals, said the US and Dutch researchers.

Interbreeding could be one reason why Neanderthals vanished, according to the scientists. They were not so much driven to extinction as assimilated.

Evidence of the two mixing can be seen in the fossil record. Some human-like characteristics have been found in late Neanderthal fossils, and conversely, Neanderthal features have been seen in early specimens of modern humans in Europe.

In the research, a group of more than two dozen species of monkeys indigenous to the forests of Central and West Africa known as guenons were examined.

Many
different species of guenons are sympatric, which means they live in close
proximity to each other, with multiple species often traveling, feeding,
and sleeping side-by-side.

He
hypothesised that sympatric guenon species underwent facial changes
that visually reinforced differences among their species in order to
avoid the risks of interbreeding - also known as hybridisation.

His theory was based on observations in the 1980s.

Researchers then
used sophisticated facial recognition algorithms that can
identify and quantify detailed features in faces to test it.

They
photographed monkeys held in captivity and employed the eigenface
technique, which is used in the field of computer vision for
machine recognition of faces.

This was used to distinguish primate features, and then to determine whether the appearance of each guenon species was
related to the appearance of other species.

Results
showed that, as predicted, the face patterns of guenon species evolved
to become more visually distinctive, specifically from those guenon
species they overlap with geographically, and hence those that they are
risk of interbreeding with.

In the research a group of more than two dozen species of monkeys indigenous to the forests of Central and West Africa known as guenons (Vervet monkeys pictured in Botswana) were examined. Despite living in close proximity, the guenons were found to be oddly diverse

'These results
strongly suggest that the extraordinary appearance of these monkeys has
been due to selection for visual signals that discourage hybridisation,' said lead
author William Allen, now of the University of Hull.

'This
is perhaps the strongest evidence to date for a role for visual signals
in the key evolutionary processes by which species are formed and
maintained, and it is particularly exciting that we have found it in
part of our own lineage.'

Assistant professor James Higham in the Department of Anthropology in New York added: 'Evolution produces adaptations that help animals thrive in a particular environment, and over time these adaptations lead to the evolution of new species.

'A key question is what mechanisms keep closely related species that overlap geographically from interbreeding, so that they are maintained as separate species.

'Our findings offer evidence for the use of visual signals to help ensure species recognition: species may evolve to look distinct specifically from the other species they are at risk of interbreeding with.

'In other words, how you end up looking is a function of how those around you look.

'With the primates we studied, this has a purpose: to strengthen reproductive isolation between populations.'